The following publications are believed to represent the current state of the art:
Microbial Fuel Cells: Methodology and Technology, Brace E. Logan et al, Environ. Sci. Technol., 40 (17), 5181-5192, 2006.
Microbial Fuel Cells—Challenges and Applications, Bruce E. Logan & John M. Regan, Environ Sci. Tech., Vol. 40, 17
Stefano Freguia, Korneel Rabaey, Zhiguo Yuan, Jurg Keller, Non-catalyzed cathodic oxygen reduction at graphite granules in microbial fuel cells, Electrochimica Acta 53 (2007) 598-603
Hong Liu et al., Quantification of the internal resistance distribution in microbial fuel cells, Environmental Science and Technology
US published patent application 20070259217